Added a load() method to allow for delayed or partial loading of a single document.
Added a load() method to allow for delayed or partial loading of a single document.

item = Model( _id=_id )
item.load( fields={'name':1})

Fixed the mongo_update method to do partial document updates correctly by default. removes the _id and wraps the document in a $set statement. Without that mongo_update() and save() would work exactly the same.

slacy/minimongo,terianil/minimongo,terianil/minimongo